The invention relates to an electric arc furnace for the production of steel by melting scrap, in particular iron scrap, and/or sponge iron and/or pig iron as well as fluxes in a furnace vessel, into which at least one graphite electrode projects, which is displaceable in its longitudinal direction, wherein an electric arc is ignited between the graphite electrode and the charging stock.
1. Field of the Invention
Conventional direct current arc furnaces for melting scrap that allow for a somewhat higher energy input comprise a single concentrically graphite electrode perpendicularly arranged in the furnace vessel. The energy input feasible, which depends on the secondary current, is limited by the maximum diameter possible of the graphite electrode. At present, a maximum energy input with furnaces of this type is feasible by means of electrodes having diameters of about 700 mm.
However, electrode diameters of this magnitude and intended larger ones call for extremely elaborate structures due to the extensive masses, forces and moments occurring and involve disadvantages during the operation of the electrode clamping device, electrode supporting arm, electrode lifting device and its guide, high-current transmission ropes, etc.
Besides, it is difficult to produce electrodes of such large diameters in sufficient quality. Moreover, the energy input via a single electric arc is concentrated on a site more or less in the center of the furnace and is rendered even more difficult by magnetic influences acting on the electric arc at high powers.
2. Description of the Prior Art
With conventional rotary-current arc furnaces, such as, e.g., those according to DE-C-29 44 269, FR-B 2 218 397 and DE-A-32 41 987, a perpendicular crater is melted into the scrap by three electrodes arranged in the center on a partial circle and the remaining scrap is dissolved thereafter. The energy of the hot offgases rises through the empty crater unutilized, thus causing excessive heating of the lid and--as also happens with conventional direct current arc furnaces--a large glowing length of the electrode, which causes intensive lateral consumption of the same. Moreover, very sturdy electrode supporting arms and lifting beams with heavy guides are necessary for the electrodes in order to control the forces and vibrations also brought about by the high currents applied. Such means constitute an essential investment cost factor, rendering the conventional rotary current arc furnace more and more expensive and its operation cumbersome.
Furthermore, it is known from EP-B-0 240 485 to provide for several plasma burners as a heating means for a furnace comprising a shaft and a consecutively arranged hearth furnace to produce steel from scrap, which plasma burners are arranged obliquely relative to the furnace axis and peripherally project inwardly from outside. However, plasma burners are limited in their efficiency by employing a tungsten electrode, and there is the constant danger of leaking water.